Scleral lens centration: The influence of centre thickness, scleral topography, and apical clearance

To investigate the effect of lens centre thickness (and mass) upon short-term horizontal and vertical scleral lens decentration, and the association between both scleral topography and apical clearance, with lens decentration.

Lens decentration was measured using over-topography data from 9 healthy young participants (25 ± 4 years) with normal corneae fitted with ICD 16.5 scleral lenses (hexafocon B material) with centre thicknesses of 150, 250, and 350 μm, while controlling for other lens parameters. Scleral toricity and elevation were determined from sagittal height data over a 15 mm chord obtained from a corneo-scleral topographer and central apical clearance was quantified using anterior segment optical coherence tomography.

The mean lens decentration was 0.55 ± 0.19 mm temporally and 0.84 ± 0.35 mm inferiorly, which did not vary significantly with centre thickness (p > 0.05). The mean nasal-temporal asymmetry in scleral elevation data was substantially greater (619 ± 67 μm) compared to the vertical meridian (369 ± 57 μm) (p < 0.01), and this variation in scleral topography along the horizontal meridian was associated with the magnitude of horizontal lens decentration (r = 0.68, p = 0.04). Greater initial central apical clearance was associated with more inferior lens decentration (r = -0.78, p = 0.01).

Lens centre thickness and mass did not significantly influence centration. Horizontal lens decentration was associated with the nasal-temporal asymmetry in scleral elevation, while vertical lens decentration correlated with initial central apical clearance. Factors affecting scleral lens centration may vary between the horizontal and vertical meridians.